This invention relates in general to mills for rolling metal products such as strands and strips. More specifically, it relates to an apparatus of compact size for rolling a narrow strip and a method of producing a thin strip.
Rolling mills are used for reducing the thickness of metal strips. The simplest rolling mill is constructed with two large and heavy work rolls rotating in opposite directions and forming a nip in between. The mill is called 2-high mill. The term “nip” is used herein to refer to the region where the rolls are closest together. The high forces associated with the rolling are guided to the work rolls bearings, which therefore have to be strong, that are heavily build. For rolling thin strips it is for contrary necessary to use work rolls with small diameter. However, with small rolls there is not enough space for strong bearings, which are required due high rolling forces. This had led to various roll arrangements in rolling mills for thin strips.
For rolling thin strips the arrangements conventionally comprises two small diameter work rolls and several support rolls, which are carrying the rolling forces and directing them through the bearings to the rolling mill frame. Usually the work rolls are at least supported by backup rolls and sometimes with a system of intermediate rolls and backup rolls. The system comprising two work rolls and two backup rolls is the most common arrangement for rolling thin strips. It is called 4-high construction. The work rolls of such construction are kept in place with small bearings whereas the rolling force is carried by support/backup rolls fitted to big heavy-duty bearings in mill frame.
4-high rolling mills are quite useful for producing the thin strip but the problem is that the heavy backup rolls are requiring a big and solid frame. The overall size of the frame of such rolling mill can be 2 to 3 meters high. The main disadvantage of such mills is that also for narrow strips the rolling mill becomes big and expensive.
Above described rolling mills are disclosed for example in following documents. US 2003/0167818 A1 discloses a hot rolling mill where a thin steel strip is passed through work rolls, which are supported by backing rolls. The construction is typical 4-high rolling mill. Such a 4-high rolling mill constructions is disclosed also in US 2002/0043358 A1.
In US 2001/0018840 are disclosed a construction with small work rolls, bigger intermediate rolls and large backup rolls. With such construction the size of the frame becomes even bigger than with 4-high rolling mill.